Fig. 1. (a) Schematic of the chemical structure of a NiPc molecule. (b) Schematic of a NiPc RRAM device with two Au electrodes on a rigid or flexible substrate. (c) SEM image of the as-fabricated device with a resistive area of 25 μ m2. (d) AFM plot of the morphology of a 15-nm-thick NiPc film. (e) Typical I-V characteristics of the device indicating the bipolar SET and RESET processes. (f) Linear fitting for the I-V curve in a double logarithmic scale showing the corresponding slopes for each part.

Fig. 2. (a) Retention and (b) endurance characteristics of the NiPc RRAMs obtained in the LRS and HRS at a constant read voltage of 0.1 V. (c) Device-to-device cumulative probability of 100 individual NiPc RRAMs of VSET and VRESET. (d) Distribution of the LRS and the HRS of 90 RRAMs.

Fig. 3. (a-b) Operation speed during SET process under a sequence bias pulse. (b) The magnified region of (a) denoted by the blue dash line indicating Δt = ～50 ns. (c-d) Operation speed during RESET process. (d) The manified region of (c) denoted by the blue dash line.

Fig. 4. (a) Optical photograph of flexible NiPc RRAMs on a PEN substrate. Scale bar is 1 cm. (b) I-V characteristics of an individual NiPc RRAM at bending strains of 0 and 0.6 %. Resistance change in the HRS and the LRS of the flexible RRAM as a function of (c) bending strain and (d) number of bending cycles. (e) Schematic of a bending substrate for the characterization of memory device flexibility. (f) The relationship between the strain and stress extracted from the flexibility simulation.

Fig. 5. (a) I-V characteristics of a single NiPc RRAM with RESET stop voltages of -1 V, -1.3 V, -1.9 V and -2.2 V. (b) Retention and (c) endurance characteristics showing four distinct intermediate HRS levels. (d) Device-to-device cumulative probability of the LRS and the HRS of 200 individual NiPc RRAMs at each level.